code: def test_expr_funcs():
      """test all functions defined in expr.funcs"""
      name_map = {val: key for key, val in expr.funcs.NAME_MAP.items()}
      for funcname in expr.funcs.__all__:
          func = getattr(expr, funcname)
          z = func(datum.xxx)
          assert repr(z) == "{}(datum.xxx)".format(
              name_map.get(funcname, funcname)
          )
  
file_path: altair/tests/expr/test_expr.py
imports: import operator
  import pytest
  from altair import expr
  from altair import datum
  from altair import ExprRef
  from jsonschema.exceptions import ValidationError
label_desc: Use image node_id 4 for calling a global function with example usage: test_expr_funcs() without return types